The art field with respect to writing instrument developed to the point where various writing instruments are available depending upon the particular job function which the instrument is intended to accomplish. Hence, it is well known that ballpoint pens have been developed which are either intended as permanent instruments, or throw away items which have a limited supply of ink, and when totally expended, are intended for throw away. In addition, ballpoint pens of the type having a number of different writing tips contained within a single barrel are known, and in the usual configuration, each of the separate barrels contains a different color ink, and each of the barrels being designed to be manipulated by control means of one form or another, such that a segregated colored ink cartridge may be manipulated into the writing position at the discretion of the user.
Other forms of writing instruments consist of felt tip pens having writing tips of various diametric dimensions which are intended for specific uses. For example, felt tip pens intended as high-lighters have been developed, usually employing a yellow ink supply and having a writing tip of a fairly substantial diametric dimension such that the user thereof may highlight various portions of a printed page for emphasis purposes. At the other end of the extreme, other forms of felt tip pens have been developed having very fine points, which are intended as writing instruments for printing characters on a page. It is well known, however, that in each and every instrument, the user must select a pen having the writing tip intended to satisfy a given function, since each of the writing instruments has a distinct tip intended for a particular purpose.
It is also well known that drafting instruments have been developed which again have variable tips contained within the same writing instrument however, in each instance, each of the different tips has a distinct diameter, and each is controlled by means of certain segregated control means to extend and retract each of the segregated writing tips. Hence, the ability to vary the diametric dimension of a drafting line is a function of extending into the writing position a particular tip having a distinct diametric dimension.
Heretofore, however, no writing instrument has been developed which has a single writing tip capable of being varied between a small and a large diametric dimension by means of appropriate control means associated therewith. It will be appreciated that there are various job functions wherein it is not only appropriate, but important to be able to vary the thickness or diameter of various line dimensions incident to the creation of that particular job function. Heretofore, no writing instrument has been developed wherein the writing tip may be varied without changing the tip. As indicated previously, while writing instruments exist which have a plurality of tips each of which may be separately controlled in order to vary the thickness of the printed or written characters, a writing instrument having a single writing tip but which is variable in diametric dimensions does not exist. It has therefore been deemed important to develop a writing instrument wherein a single tip may be employed, but which tip may be alternately varied between a small and large dimension by means of a single control means incorporated within the design and construction of the instrument.